The Genetics of Familial Polyposis

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1 The Genetics of Familial Polyposis Thursday, September 24 th 2015 Kara Semotiuk, MS, (C)CGC & Laura Winter, MSc, CGC Genetic Counsellors at the FGICR

2 Familial Polyposis Familial Can run in the family related to our genes Polyposis Multiple polyps Polyp: non-cancerous growth, inside the GI system Different types of polyps Adenoma: Risk to become cancer if not removed TODAY: FAP & MAP

FAP: Familial Adenomatous Polyposis Classic FAP: 100s-1000s of colorectal adenomas, onset as early as childhood/adolescence Can also be polyps in small bowel (duodenum) &/or stomach Somewhat higher

3 FAP: Familial Adenomatous Polyposis Classic FAP: 100s-1000s of colorectal adenomas, onset as early as childhood/adolescence Can also be polyps in small bowel (duodenum) &/or stomach Somewhat higher risk for other cancers including thyroid Non-cancerous features: desmoids, CHRPE, osteomas, skin cysts, extra teeth Attenuated FAP (AFAP): less severe, fewer polyps (< 100), later onset Both FAP and AFAP are rare seen in only 3 per 100,000 people Both are caused by changes in the same gene called APC

Genetics Cell Genetic testing is usually done on DNA collected

Mutation: change in the code APC gene ONE Mutation affected

numbers Location of mutation in gene associated with classic

4 Genetics Cell Genetic testing is usually done on DNA collected from a blood sample DNA Many genes Genes written in code Mutation: change in the code APC gene ONE Mutation affected Autosomal dominant inheritance Affects males & females in equal numbers Location of mutation in gene associated with classic FAP vs. AFAP Two copies of each gene One copy inherited from mom, one from dad

5 FAP: Dominant Inheritance Parent with FAP Mutation in 1 APC gene What age to test? When screening starts: FAP: yr AFAP: yr 50% (1 in 2) chance for each child to inherit FAP/AFAP

6 Inherited vs. de novo Affected parent Unaffected parents 75-80% of time FAP is inherited from a parent 20-25% of time FAP starts new in a child

If a child inherits a mutation in APC They have FAP / AFAP Screening for colorectal polyps Classic FAP: age 10-12 AFAP: age 18-20 Surgery if

7 If a child inherits a mutation in APC They have FAP / AFAP Screening for colorectal polyps Classic FAP: age AFAP: age Surgery if too many polyps to manage by colonoscopy Screening of remaining colon/rectum/pouch Upper GI screening from ~age 25 Annual thyroid palpation by GP

8 If a child did not inherit APC mutation - They do not have FAP/AFAP - They cannot pass it down to children - Population cancer screening (unless other family history) Importance of informing relatives about genetic testing: FAP screening vs. general population screening Parents, siblings, children, others

9 MUTYH-Associated Polyposis (MAP) MAP vs. (A)FAP Clinical presentation is similar: Multiple adenomatous polyps In MAP, other types of polyps such as hyperplastic or serrated polyps that can be seen in addition to adenomas polyps by age 50 on average 100 s to 1000 s of polyps in some cases Gene is different: MUTYH (MYH) Inheritance is different: Autosomal RECESSIVE inheritance

10 Recessive Inheritance If both parents are carriers (unaffected), each child has a 25% (1 in 4) chance of having MAP Brothers and sisters of someone with MAP have a 25% (1 in 4) chance of also having MAP

11 For Someone With MAP Very small chance for children to have MAP Only possible if spouse/partner is a carrier (or has MAP) - very unlikely Who should get tested in the family: Spouse/partner If negative, children don t need testing Children, if spouse/partner not available Brothers & sisters

MAP Screening 2 mutations (MAP) Colonoscopy every 2-3 years beginning at 18-20 Every year once polyps

12 MAP Screening 2 mutations (MAP) Colonoscopy every 2-3 years beginning at Every year once polyps detected Side-viewing upper endoscopy every 5 years or more often depending on findings, beginning at 25-30

13 Population Screening Or No mutation or 1 mutation (carrier): BOTH UNAFFECTED Not at significantly increased risk for polyps/cancer Follow population cancer screening unless other family history of polyps or cancer

14 Summary FAP and MAP both cause multiple polyps, BUT: Different genes (APC vs. MUTYH) Different inheritance (Dominant vs. Recessive) Different screening recommendations Genetic testing has improved over the years You may be eligible for further testing if: Your genetic testing was many years ago or your never had genetic testing You have multiple polyps and had genetic testing where nothing was found

15 Genetic Questions? *** Speak to your genetic counsellor *** Dr. Zane Cohen (centre), with genetic counsellors (L to R) Melyssa Aronson, Spring Holter, Kara Semotiuk & Laura Winter

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